The invention relates generally to an FM data recorder and a method for recording a data signal and playing it back and more particularly to an FM data recorder and the method for recording a data signal received from a miniature test model under test, the miniature model representative of an actual real life model. The recorded information is played back, by control of a speed control signal, at a speed ratio directly proportional to the size ratio between actual size and miniature size.
In a conventional FM data recorder and method for recording a data signal and for playing it back at a different speed ratio from the recorded speed, the speed ratio between the recording and playback speeds is not variable. Therefore, the playback speed is not directly and linerly proportional to the input data signal and input speed control signal contrary to prior art.
Whereas, in the FM data recorder and method for recording a data signal from a miniature test model and for playing it back of the present invention, a vibration signal and/or the like received from the miniature test model indicates the strength, the character and/or the like of the miniature test model which would be representative of a real life model or actual structure such as a building, dam or the like.
When a big structure such as a dam is to be constructed, a miniature test model thereof is tested instead of an actual real life model, as it is almost impossible to construct such a big actual life model for the test. However, the data signal from a miniature test model under test is, of course, different from the data signal which would be received from an actual real life model if it was tested, as they are different in size. Consequently, the data signal from a miniature test model under test should be converted into a data signal which is representative of an actual real life model or actual structure. However, the ratio in size between the miniature test model and the actual structure has to be an "integral number" such as one tenth, one twentieth, etc., because of easier computation in constructing the miniature test model. The ratio data signal between input (recording) and output (playback) as a function of an input data signal, such as a vibration signal, between the miniature test model and the actual structure is directly proportional to the "square root" of size ration between the miniature size and actual life size. Consequently, it is necessary to achieve such a "square root" ratio.
A conventional FM data recorder, however, records a data signal from a miniature test model under test and plays it back at an "integral" speed ratio, so that the played back data signal is "similar" to that which would be received from a real case (i.e. if the actual structure would be put under test). Whereas, this invention employs an FM data recorder which records a data signal from a miniature test model under test and which plays it back at a square root ratio in speed, so that the played back data signal is the "same" as that which would be obtained if the actual structure would be put under test.
As mentioned above, the conventional FM data recorder has an integral ratio in speed between recording a data signal and playing it back. For example, the ratio is 1:2:4:8:16:32, 1:2:5:10:20 or the like. However, when a miniature test model is one tenth as small as an actual structure in size, the real ratio of data received between them is the square root of 10 or 3.1623 - - - . Consequently, a conventional FM data recorder cannot play back a data signal perfectly equivalent to data which would be recorded from an actual structure, since a conventional FM data recorder does not account for the required ratio in speed unless it is made especially for such a ratio.
Furthermore, if presently available FM data recorders are compensated for the square root problem, a different FM data recorder will be required for each different size ratio between a miniature test model and an actual structure thereof, since the size ratio of one combination, such as a building and a miniature test model, is different from the size ratio of another combination, such as another building or a dam and a miniature test model thereof.
On the other hand, the present invention employs a recording speed control signal which controls the recording speed of the FM data recorder and is simultaneously recorded with a data signal on a record medium such as a magnetic tape, and the playback speed is controlled by a variable speed control signal for playback; thus, it is possible to achieve any speed ratio between the recording speed and playback speed. Accordingly, desired data at a desired speed ratio can be read out when it is played back.
The reason why a conventional FM data recorder requires a non-variable speed means is that it requires a good S/N ratio. As in FM broadcasting, the FM data recorder has a carrier frequency wave (fo) which is modulated by an input data signal (Ein). The frequency-modulated carrier wave (fo.+-..DELTA.f) is recorded on a magnetic tape through the write amplifier. When it is played back, the read head reads or reproduces the frequency-modulated carrier wave, which is then demodulated to obtain a data signal, and a conventional mechanical variable speed control means creates a lot of noise or wow and/or flutter due to the inevitable unstable speed of the mechanism.
It is therefore necessary to maintain a stable tape speed. If the tape speed of the FM data recorder is unstable, the carrier wave is modulated by the input data signal (Ein) as well as by the variation of the unstable tape speed.
This can be represented by the formula: EQU fo.+-..DELTA.f.+-..DELTA.S
When the tape speed is too unstable, the variation in unstable tape speed (.DELTA.S) exceeds the input data signal (.DELTA.f). Whereas, wow and/or flutter is/are required to be lower than 0.4%, the tape speed is required to be stable in order to improve the S/N ratio.
Furthermore, a conventional FM data recorder is not able to linearly vary the tape speed but only able to step the tape speed up or down with a mechanical step means or switching steps of the motor speed.
On the other hand, the present invention employs a means for linearly varying the tape speed, and can therefore achieve any speed ratio, e.g.--the square root of 10 or 3.1623 - - - , between the recording speed and the playback speed. However, it does not mean the tape speed is varied "during" recording or playback. It must be stable "during" that time. It can be varied "before" beginning the recording of a data signal or before playing it back, so that a desired speed ratio, such as 3.1623 - - - , between the recording speed and the playback speed can be achieved to perfectly represent the ratio in size between a miniature test model and an actual structure, such as a dam, building and the like.